Black circles animate in an undulating horizontal line across a black-and-white SVG canvas. Using D3 v7, the visualization demonstrates the selection, enter, update, and exit lifecycle with a compact `.join()` pattern that creates or removes circles based on a fluctuating count. Data is generated live with `d3.range` and trigonometric functions, while `setInterval` drives the animation at about 60 frames per second, adjusting each circle’s x and y positions over time.